The concept of irrigation drain valves is known in the art and typical of such drain valves are those shown in King U.S. Pat. Nos. 5,163,779; 5,080,527 and 4,890,640.
Typically, an irrigation system includes a set of spaced, above ground sprinkler heads and underground water supply lines that supply water to the sprinkler heads. In climates where the water can freeze, a set of drain valves are placed at the lowest points of the water supply lines to allow water remaining in the water supply lines to drain out of the water supply lines in order to prevent freeze damage to the water supply lines.
The drain valves, which are located underground and at the lowest points in an irrigation system generally contain an elastomer member, which is mounted over a drain port in the irrigation drain valve. Under a no or low water pressure condition the elastomer is spaced from the drain port thereby allowing water to drain through the drain port. However, as the water supply line pressure increases the pressure within the drain valve also increases which forces the elastomer member against the drain port thereby sealing the drain port and preventing water from draining from the drain valve. Sealing the drain port allows all the water to be directed to the water sprinkler heads. Correspondingly, when the water pressure decreases i.e. the water to the water supply lines is shut off; the resilient elastomer retracts thereby opening the drain ports to allow water in the lines to drain through the drain ports. Thus, an irrigation system with pressure sensitive drain valves automatically drains the water in the water supply lines once the water supply lines are shut off.
While such systems are well suited for colder climates where freezing water can damage the irrigation system the drain valves can allow a substantial amount of water to be wasted during an irrigation season since the drain valves direct the drain water underground and not necessarily to the areas needing irrigation. If some locations water is scarce and a need exists to wisely use the available water. The invention described herein allows water to drain from the drain valve when freezing conditions occur but prevents water from draining from the water supply lines when freezing conditions are not present thus conserving water.
Thus a feature of the invention is a water-saving drain valve having two operating modes, an above freezing mode wherein the drain valve normally remains closed regardless of whether the system water pressure is on or off in order to prevent loss of water from the system and a second near freezing mode wherein the drain valve functions as a conventional drain valve that closes in response to a high system water pressure and opens in response to a low system water pressure to thereby drain the irrigation system and prevent freeze damage.